ECU hold power wiring

[MGV101]

I'm trying to setup ECU hold power solely for the purpose of keeping the engine bay fans running after I have switched the ignition off.

I noted in the examples from the help file, a second relay is used to power the igniton coils, injectors, solenoids etc. to keep them powered up together with the ECU with the ignition off.

As I am only using ECU hold power to keep the ECU powered up controlling my fan relays with GP outputs and temperature sensors, can the second relay be omitted and have the ignition coils, injectors, solenoids etc powered by its stock power system which switches off once the ignition is switched off? Would there be any negative effect if the ECU is powered on while everything else had been powered down?

 

Thank you!

Edited September 21, 2017 by MGV101

[b3tuning]

I'm trying to setup ECU hold power solely for the purpose of keeping the engine bay fans running after I have switched the ignition off.

I noted in the examples from the help file, a second relay is used to power the igniton coils, injectors, solenoids etc. to keep them powered up together with the ECU with the ignition off.

As I am only using ECU hold power to keep the ECU powered up controlling my fan relays with GP outputs and temperature sensors, can the second relay be omitted and have the ignition coils, injectors, solenoids etc powered by its stock power system which switches off once the ignition is switched off? Would there be any negative effect if the ECU is powered on while everything else had been powered down?

 

Thank you!

You have to be careful with the wiring when using ecu hold power.  The reason for the second relay(s) is to prevent a circuit back feeding power into the ecu and preventing proper shut off.  If the ecu is controlling the relays powering ancillary devices (solenoids, coils, injectors, etc) via a low side output (Aux Out), then there will be no issues.  

You could also probably use the fan setting RPM Zero Timeout to achieve what you need without using ECU Hold Power and the extra wiring

[MGV101]

Thanks you, everything should be powered from the low side but I'll double check to make sure.

The problem with RPM Zero Timeout is that it only works if they ECU is powered up so it will require ECU hold power to function too.

 

Also another problem with the engine fan control on the Link ECU is that it is designed to control the radiators fans only as it is dependent on ECT. I am trying to control the engine bay temperatures on a mid engine car so controlling the temperature with reference to ECT is actually not very useful to me. I had use GP outputs and virtual aux to setup my own fan control with sensors in the engine bay. Would be nice if Link could give us the option to change the inputs under the default engine fan control.